Induction heating stress improvement

ABSTRACT

In implementing an induction heating stress improvement (IHSI) method in a nuclear plant, cooling characteristic with respect to the inner surface of piping is improved by appropriate structure/layout of nozzles, and further, the cooling effect when applying IHSI to a real machine is verified by installing a thermometer, as well as air in the portion subjected to IHSI is removed by heating the piping prior to the execution of IHSI.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an induction heating stress improvement method (hereinafter abbreviated as “IHSI” method) in a primary loop recirculation piping (hereinafter abbreviated as “PLR” piping) of a nuclear power plant.

2. Description of the Related Art

As an example of conventional IHSI method for a double metal, there is a method disclosed in JP, A 2-282428. In this conventional art, water flows are alternately spouted into an annular space, and the nozzle outer surface surrounding the annular space is heated to give a temperature difference to the nozzle wall, whereby residual stress is relaxed.

Conventional inventions, however, have involved a problem in that they have indeed exerted an enhanced cooling effect but have been incapable of verifying a cooling effect when applying IHSI to an actual machine. Particularly in a recirculation inlet nozzle (hereinafter referred to as an “N2 nozzle”) having a narrow annular clearance, it is very difficult to spout a fluid to produce a flow in the annular clearance. Furthermore, the inner surfaces of piping of actual machines would have various asperities depending on individual piping although these are slight asperities to the extent presenting no problem in terms of performance and structure of the machines, and/or the surface of the outer surface of the piping might not be a perfect circle in the cross-section thereof. As a result, it is difficult to dispose a cooling nozzle apparatus in the reactor in a proper position, thereby causing a possibility that the nozzle may not be directed toward the direction of the annular clearance. Hence, as a matter of fact, it is necessary to verify, in the actual machine, whether a jet is sufficiently flowing into the annular clearance. That is, it is important to verify a cooling effect with respect to the inner surface of the piping when applying IHSI to the actual machine, as well as a contrivance to cause jet to efficiently flow into the narrow annular clearance is needed.

Conventional inventions require a plurality of devices such as a large number of jet nozzles, piping for use in connection, and the like, in order to secure a sufficient cooling effect. In a nuclear power plant, a rationalized apparatus is desired from the viewpoint of reducing radioactive waste to a minimum. If use of such a rationalized apparatus allows a cooling effect to be verified, and a jet to be efficiently flowed into the annular clearance, then the number of the above-described redundant devices can be reduced.

Furthermore, in the PLR piping of a reactor, a flange or an air vent cannot be installed in the viewpoint of safety ensuring and leakage prevention. As a consequence, air could stagnate in a closed stagnation portion such as nozzle to decontaminate, and might make impossible the water cooling when executing IHSI, which entails the removal of air. This is because air is very low in thermal conductivity and heat transfer coefficient, and exerts a significant detriment to the execution of IHSI. Such stagnant air cannot be removed by only water flows, which has constituted a problem associated with the application of IHSI.

SUMMARY OF THE INVENTION

To solve the above-described problems, a thermometer is installed to a cooling apparatus for IHSI to measure the temperature of a fluid subjected to a temperature rise by cold removal. By measuring the temperature of a fluid flowing out from the annular clearance by a jet from the fluid nozzle, it is possible to verify a cooling effect in an actual machine. Using in advance a computational fluid dynamics analysis or tests, the relationship between the fluid temperature distribution in the annular clearance (the fluid temperature in a portion subjected to IHSI is especially important) and the temperature of fluid flowing out from the annular clearance is determined. If the temperature measured by the thermometer is a predetermined estimated temperature, it is considered that a heated surface is being cooled by a forced convection by the nozzle. On the other hand, if the temperature measured by the thermometer is shifted from the estimated temperature, it is considered that the forced convection by the nozzle is not effectively working. For example, let's execute IHSI by an algorithm shown in FIG. 3. Since the occurrence of boiling of fluid in the annular clearance makes cooling impossible, it is especially important that the temperature of the fluid in the annular clearance is not more than the saturate temperature thereof.

If a characteristic graph and/or relationship diagram for estimating a maximum temperature and/or temperature distribution on the inner surface of piping versus the temperature of the fluid discharged from the annular clearance in response to an amount of flow supplied from the nozzle, is prepared in advance, then it would be readily found out, in the process of executing IHSI operation, that a cooling effect with respect to the inner surface of the piping is being obtained. That is, it becomes clear in real time that the operation is a proper one.

Unless positions in the peripheral direction, of the cooling nozzles and a position of the thermometer to be installed are properly laid out, the temperature of the fluid flowing out from the annular clearance cannot be measured, and an estimated temperature evaluation might become impossible. In this case, it is necessary to install a thermometer such as a thermocouple at a position from which a high-temperature fluid flows out. To this end, the installation position of the thermometer must be deviated from that of the cooling nozzles in the peripheral direction.

While the foregoing description mainly concerns the verification of cooling effect, study of shapes and the like of nozzle is required in order to satisfy a reliable cooling effect by efficiently flowing a jet into the annular clearance.

One of methods for satisfying a reliable cooling effect is a case in which nozzles are installed at an upper portion of a cylinder. In this method, on the tangential surface (a range in which jets from the nozzles are accommodated within the annular clearance) in the peripheral direction, of an inner cylinder, the nozzles are each tilted from the surface in the horizontal direction toward the cylinder center line (the line connecting the upper and lower ends the cylinder). This tilting allows the area occupied by a coolant jetted from the nozzles to move to the center of the annular clearance, and turbulence to be amplified by interference between two jet flows. Test results with an actual machine-sized model showed that an angle of tilt of 9 degrees provides an optimum result.

Furthermore, in this case, the nozzles are not installed in a structure adjacent to the cylinder, but a hole for coolant jetting is made in the structure itself to issue jet flows from the hole. Herein, in order to increase the speed of jet flows, the hole needs a narrowed portion.

Also, insertion of the tip of the nozzles into the annular clearance allows jets to be reliably flowed into the annular clearance, thereby enhancing cooling effect.

When the annular clearance is especially narrow, it is desirable to use a method in which a structure (pad) having a seal mechanism along the inner cylinder is covered, and in which a coolant is flowed into the annular clearance along a flow path formed between a structure (pad) provided along the outer surface of the inner cylinder and the outer surface of the inner cylinder, to promote cooling effect. Thereby, a flow along the outer surface of the inner cylinder is formed, which enables a flow to be generated even in the narrow annular clearance.

Use of a sink flow prevents flows from becoming local flows like jet flows, thereby promising to produce a stable cooling effect. Also, by varying the flow rate and pressure using the variation in the revolution number of a primary loop recirculation (PLR) pump and/or the variation in the opening of valves, the cooling effect can also be improved.

As a method for removing air when executing IHSI, the present invention executes the following means. The area that most requires the removal of air is a nozzle to decontaminate. In general, non-condensing gas such as air, having a low density, stagnates at an upper portion of a pipe, so that air cannot be removed by water flows. The present invention has implemented removal of air using the following procedure. First, the water flows are stopped or water is flowed at a low flow rate, with the piping heated from the outside. Upon arrival at its saturation temperature, water in the piping evaporates into water vapor. Since the water vapor is lower in density than air, air stagnant in an upper portion is gradually pushed out by water vapor. That is, because the evaporation of water increases the volume thereof by a factor of 1000, air is easily pushed out by the water vapor. As a result, the nozzle to decontaminate is filled with water vapor. Next, upon stopping heating and starting cooling, the temperature of the water vapor decreases and the water vapor starts to condense. When the water vapor decreases in temperature, it is totally subjected to a state change into water, so that the nozzle to decontaminate is filled with the water. As a consequence, non-condensing gases, air, and the like could be totally removed from the nozzle to decontaminate. Thus, the execution of IHSI enables air in the stagnant portion such as the nozzle to decontaminate to be totally discharged. Meanwhile, the speed of water flow is different between the time when IHSI is executed and the time when air removal is performed. When executing IHSI, the highest possible flow rate is needed in order to suppress boiling and cool the inner surface of the piping, but when performing air removal, it is necessary to make the flow rate 0 or low in order to boil water. Valves are provided in front of and behind the annular nozzle to decontaminate, and therefore, when performing air removal, it is desirable to heat the nozzle to decontaminate in an enclosed state or somewhat closed state, making use of the valves. As described above, the present invention has solved the above-described problems by taking advantage of physical properties of air and water vapor and the state change of water vapor.

By the application of the present invention, it is possible to secure the inner surface cooling when applying IHSI to an actual machine can be secured, and to reliably relax residual stress at PLR piping welded portion. This allows more reliable execution of IHSI to be implemented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a piping cooling technique in IHSI according to the present invention;

FIG. 2 is a schematic diagram of analysis results of temperature distribution in an annular clearance of recirculation inlet nozzle.

FIG. 3 is a flowchart of implementation procedure for IHSI according to the present invention;

FIG. 4 is a flowchart of operational steps for deriving the relation ship between the temperature distribution in the annular clearance and the outflowing fluid temperature.

FIG. 5 is a schematic diagram of a piping cooling technique in IHSI according to the present invention;

FIGS. 6A and 6B are schematic diagrams of a piping cooling technique in IHSI according to the present invention;

FIG. 7 is a schematic diagram of a piping cooling technique in IHSI according to the present invention;

FIG. 8 is a schematic diagram of a piping cooling technique in IHSI according to the present invention;

FIG. 9 is a schematic diagram of a piping cooling technique in IHSI according to the present invention;

FIG. 10 is a schematic diagram of a piping cooling technique in IHSI according to the present invention;

FIGS. 11A and 11B are schematic diagrams of a piping cooling technique in IHSI according to the present invention;

FIG. 12 is a schematic diagram of a piping cooling technique in IHSI according to the present invention;

FIG. 13 is a schematic diagram of a piping cooling technique in IHSI according to the present invention;

FIG. 14 is a schematic diagram of a piping cooling technique in IHSI method according to the present invention;

FIG. 15 is a schematic diagram of a piping cooling technique in IHSI according to the present invention;

FIG. 16 is a schematic diagram of a piping cooling technique in IHSI according to the present invention;

FIG. 17 is a schematic diagram of a piping cooling technique in IHSI according to the present invention;

FIG. 18 is a schematic diagram of a piping cooling technique in IHSI according to the present invention;

FIG. 19 is a schematic diagram of a piping cooling technique in IHSI according to the present invention;

FIGS. 20A and 20B are schematic diagrams of analysis results of temperature distribution in a nozzle to decontaminate;

FIGS. 21A to 21D are schematic diagrams explaining a principle of air removal technique in the induction heating stress improvement according to the present invention;

FIG. 22 is a flowchart of implementation procedure of the air removal technique in IHSI according to the present invention;

FIG. 23 is a schematic diagram of a piping cooling technique in IHSI according to the present invention;

FIG. 24 is a flowchart of implementation procedure for IHSI according to the present invention;

FIG. 25 is a schematic diagram of an N2 nozzle cooling technique in IHSI according to the present invention, as viewed from the side surface of an N2 nozzle portion;

FIG. 26 is a schematic diagram showing the N2 nozzle cooling technique in IHSI according to the present invention, as viewed from the top surface of the N2 nozzle portion;

FIG. 27 is a schematic fluid outflow characteristic view under the N2 nozzle cooling technique in IHSI according to the present invention; and

FIGS. 28A and 28B are flow velocity vector views showing a jet oscillation characteristic under the N2 nozzle cooling technique in IHSI according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A piping cooling technique in IHSI method according to the present invention will be described with reference to FIG. 1. FIG. 1 is a constructional view of a recirculation inlet according to an embodiment of the present invention. The recirculation inlet comprises an N2 nozzle 1, a thermal sleeve 2 therein arranged, and a riser tube 3 serving as a jet pump and connected to the thermal sleeve 2. At a welding portion 4 in the N2 nozzle 1, the residual stress can be relaxed by the execution of IHSI method. This enables enhancement of the safety of nuclear power. The IHSI method is a method for heating the surface of the outer surface of the piping by a heater 5 provided in the outer surface of the piping and cooling the inner surface of the piping by water in the piping, whereby residual stress is relaxed by a thermal gradient in the cross-section of the piping. When the piping is of a pure straight pipe, the inner surface of the piping is sufficiently cooled, and there is no problem. However, in an annular clearance 6 on the piping inner surface at the welding portion, since the flow stagnates, fluid temperature increases by the heating from the outside, so that the inner surface of the piping could not sufficiently cooled. With this being the situation, in this embodiment, at least one nozzle 8 is installed and is caused to jet cooling water toward the direction of the annular clearance, thereby cooling the heated inner surface of the piping. Also, in this embodiment, at least one thermometer 9 is installed to measure a fluid temperature. Two nozzles 8 are arranged in a horizontal direction, and one thermometer is disposed above the nozzles, that is, in a state where they are displaced from one another. Cooling water is driven by a circulating pump 10 provided outside a reactor, and jetted from the nozzles 8 through the piping 11. As indicated by arrows in FIG. 1, the jet flows of the nozzles 8 arranged in the horizontal direction (3 o'clock direction and 9 o'clock direction) are jetted toward the welding portion 4, and are flowed into the reactor from the upper side and lower side (0 o'clock position and 6 o'clock position) of the annular clearance. With the direction of flow considered, regarding the outside of the annular clearance (i.e., the outside of intersection points between the outer periphery of the annular clearance and the lines of 45 degrees and 135 degrees), above-described regions are mutually distinguished by lines extending upward (to the upper side) from the above-described intersection points. Furthermore, installation of the thermometer 9 to the cooling apparatus eliminates the need for a structure for use in a new thermometer or an apparatus for guiding the flow in the reactor. Here, it would be desirable to install the nozzles on the rear surface, side surface, or bottom surface of the cooling apparatus rather than on the front surface, since flows issued from annular clearance flow can easily cross the thermometer on the above-described rear, side, or bottom surface. However, front surface positions that are located higher than the top end of the annular clearance could be used as nozzle installation positions without problem. Also, the temperature measurement may also be performed in the RPV.

FIG. 3 shows IHSI steps in embodiments according to the present invention. These steps will be described below.

(Step 100) IHSI is started.

(Step 101) As will be described later, the relationship between the annular clearance strength distribution and the temperature of outflowing fluid is derived.

(Step 102) Nozzles for IHSI are installed to an actual machine, and a fine adjustment of nozzle positions and a flow rate adjustment are performed.

(Step 103) The temperature of fluid flowing out when IHSI is executed is measured by a temperature sensor.

(Step 104) An annular clearance temperature distribution is calculated/estimated by a computer, based on the temperature of the outflowing fluid, measured by the temperature sensor.

(Step 105) It is calculated and determined by the computer whether the annular clearance temperature is not more than a predetermined temperature (fluid saturation temperature). Also, at step 105, a command indicating that the annular clearance temperature has not yet arrived at a temperature of not more than predetermined temperature, returns to step 102, and a fine adjustment of nozzle positions and a flow rate adjustment are performed again to execute IHSI.

(Step 106) It is verified that the, in step 104, IHSI has been executed under the condition the annular clearance temperature is not more than a predetermined temperature, and thereupon IHSI process is completed.

FIG. 2 shows a temperature distribution at this time in the annular clearance. Under natural convection, a high-temperature fluid moves to an upper portion of the annular clearance while a low-temperature fluid moves to a lower portion thereof. In particular, in the back region of an upper portion of the annular clearance, high-temperature water stagnates. As a result, when a flow as shown in FIG. 1A occurs, the high-temperature water heated by a heater crosses high-temperature the thermometer disposed at an upper portion. If the flow assumed in FIG. 1A does not occur, the high-temperature water does not cross the thermometer. Therefore, flow occurring at the heater portion can be estimated from the temperature value measured by the thermometer, and thereby presence of a cooling effect can be verified. For particulars, using in advance a computational fluid dynamics analysis or model tests, the relationship between the fluid temperature distribution in the annular clearance and the fluid temperature flowing out therefrom is determined, which makes it possible to perform a high-accuracy evaluation. Of course, it is also advisable to prepare in advance a characteristic graph allowing estimating a maximum temperature and/or temperature distribution on the inner surface of piping, from the temperature of the fluid flowing out therefrom in response to an amount of flow supplied from the nozzles.

In executing the above-described IHSI method according to the present invention, processing shown in FIG. 4 is performed in advance, in order to derive the required relationship between the fluid temperature distribution in the annular clearance and the temperature of outflowing fluid. These processing steps will be described below.

(Step 200) The derivation of the relationship between the fluid temperature distribution in the annular clearance and the temperature of outflowing fluid is started.

(Step 201) A mockup of an actual machine to be subjected to IHSI is created.

(Step 202) Nozzles for supplying water flows to the mockup created in step 201 and various sensors such as a water-pressure gauge, water meter, and thermometer are installed.

(Step 203) The mockup is arranged in a test tank.

(Step 204) Water flows are supplied to the mockup and IHSI is executed.

(Step 205) Temperatures, water flow temperatures at various places in the mockup, and various measurement conditions, such as water pressure of water flows, and the pressure in a pump, are calculated, and the calculated data is stored into the computer.

(Step 206) The derivation of the relationship between the fluid temperature distribution in the annular clearance and the temperature of outflowing fluid is completed.

In this manner, by deriving the relationship between the fluid temperature distribution in the annular clearance and the temperature of outflowing fluid in the mockup, it becomes possible to derive the relationship between the fluid temperature distribution in the annular clearance and the temperature of outflowing fluid in the actual machine to be subjected to IHSI.

FIG. 5 shows an embodiment in which the layouts of the thermometer 9 and the nozzles are mutually interchanged. In this embodiment also, an effect similar to that in FIG. 1 can be obtained. Specifically, fluid flowing into the annular clearance and fluid flowing out therefrom is equal in amount, and hence as shown in FIG. 5, it is necessary to lay out the thermometer and the nozzles so as to be mutually spaced apart. FIGS. 6A and 6B show an example of possible layout method for thermometer and nozzles. As shown in FIG. 2B, since high-temperature fluid stagnates in an upper portion, when the nozzles are arranged in the range within ±45 degrees from the horizontal direction (3 o'clock direction and 9 o'clock direction) shown in FIG. 6A, the range within ±45 degrees from the position of 0 o'clock position at an upper portion becomes an outflow direction, and therefore the thermometer is installed within this range. At this time, however, in the range within ±45 degrees from the position of 6 o'clock in a lower portion, the nozzles or the thermometer is difficult to install. Therefore, when the nozzles are arranged in the range within ±45 degrees from the position of 0 o'clock in an upper portion shown in FIG. 6B, the thermometer is disposed within the range of ±45 degrees from the horizontal direction (3 o'clock direction and 9 o'clock direction). As described above, laying out the thermometer and the nozzles so as to be mutually spaced apart allows an effective measurement of fluid temperature. Here, the number of nozzles (or a nozzle) is not limited. Also, installation of the thermometer or nozzles in a lower portion (6 o'clock position) does not particularly present a problem, but in this case, way of installing them is very difficult. Hence, as shown in FIG. 1B, it would be more desirable to arrange the nozzles in the region in the horizontal direction (3 o'clock direction and 9 o'clock direction) and make the direction from 0 o'clock to 6 o'clock an outflow direction, in that the nozzles can be arranged in substantially a symmetrical manner. In other words, by arranging the nozzles substantially symmetrically in the region in the horizontal direction (3 o'clock direction and 9 o'clock direction), the imbalance in the cooling characteristics of nozzles can be reduced to a minimum. This facilitates the evaluation of temperature distribution, and enhances the cooling effect by the suppression of the imbalance of cooling effect, thereby enables the annular clearance to be cooled with a minimum flow rate. Moreover, since the high-temperature portion in the annular clearance is located at an upper portion, high-temperature fluid flows out, and the thermometer disposed at an upper portion can measure temperature with high accuracy. With the direction of flow considered, regarding the outside of the annular clearance (i.e., the outside of intersection points between the outer periphery of the annular clearance and the lines of 45 degrees and 135 degrees), above-described regions are mutually distinguished by lines extending upward (to the upper side) from the above-described intersection points. Furthermore, it is desirable from a production view point that the thermometer is installed to the cooling apparatus. Also, it would be desirable to install the nozzle on the rear surface, side surface, or bottom surface of the cooling apparatus rather than on the front surface, since flows issued from annular clearance flow can easily cross the thermometer on the above-described rear, side, or bottom surface. However, a front surface area that is located higher than the top end of the annular clearance could be used as nozzle installation positions without problem.

In particular, it is difficult to flow a jet into the narrow annular clearance. Such being the case, a method for efficiently flowing a jet into the narrow annular clearance will be described below. In this embodiment, as shown in FIG. 7, nozzles are installed at an upper portion of a cylinder, are tilted θ degrees to the direction of the cylinder center line (the line connecting the upper and lower ends the cylinder). This tilting makes it possible to move the area subjected to jetted by the nozzles to the center of the annular clearance, and amplify turbulence by interference between two jet flows. As a result, because the flow runs around to the lower end of the annular clearance, cooling effect is enhanced. Particularly in the model test, tilting of 9 degrees allowed collided jet flows to arrive even at the lower end of the annular clearance, thereby providing optimum cooling. Also, as shown in FIG. 8, by tilting the nozzles to the outside and a little downward, an effect is obtained, as well. As described above, addition of a tilt component in the tangential direction to the cylinder, which has not been hitherto taken into consideration, enhances a cooling effect. Particularly, in this embodiment, combining a tilt of a cylinder center direction component would not present a problem.

FIGS. 9 to 11 are diagrams showing embodiments regarding nozzle portions of the cooling apparatus. These diagrams are depicted with reference to FIGS. 7 and 8. In each of FIGS. 7 and 8, nozzles are actually tilted, but here, for convenience in explaining, these diagrams are referred to, on the assumption that the nozzles be not tilted. The nozzle portion of cooling apparatus shown in FIG. 9 is characterized in that, regarding a cooling apparatus using an induction heating stress improvement method, in a structure constituting the bottom of a cooling apparatus in the vicinity of the inner cylinder of an N2 nozzle, there is provided a cave hole flow path forming a flow path exit (nozzle) from which a coolant is to outflow, and that the coolant is flowed from the flow path exit into the annular clearance, to promote cooling effect. In this embodiment, a narrowed portion 19 having a cross-sectional area decreasing toward an exit direction of the nozzle is provided in order to accelerate a fluid. An ordinary narrowed portion or enlargement portion is axisymmetric, and hence the distance between the bottom surface and the nozzle center is large in the minimum area portion thereof, so that it is impossible to flow jet flows into the narrow annular clearance. In this embodiment, particularly for the purpose of flowing jet flows into the flow path of the narrow annular clearance, the upper portion of the nozzle is greatly narrowed, with the cross-sectional area in the upper portion significantly changed, and the lower portion thereof is formed into a non-axisymmetric shape such as to retain a substantially flat shape. This provides a structure allowing an achievement of optimization of a coolant jetting position, thus ensuring the issuing of jets into the narrow annular clearance. Moreover, by virtue of the above-described shape, flows are directed toward the center of the inner cylinder, so that the direction of flows can be controlled, a further effect Here, possible narrowed portions include, e.g., an orifice-shaped one. The structure in which a hole for the nozzle is formed, may be made up by combining some components, besides it constitutes a single-piece construction.

FIG. 10 shows an embodiment characterized in that a header tank is arranged on the bottom surface; a plurality of flow paths forming outflow openings (nozzles) 8 for allowing a coolant to flow out is formed at substantially the lowermost end of the header; and the coolant is flowed into the annular clearance to promote cooling effect. This embodiment, therefore, has a structure effective in providing a large number of nozzles 8 with respect to the header tank. It is further desirable that the nozzles be replaceable. Also, by this embodiment, the number of pipes for conveying the coolant can be reduced. Furthermore, since fluid pressure operating on each nozzle is rendered uniform, fluid amount control with respect to each nozzle can be easily performed. In addition, the above-described features allow jets to flow into the narrow annular clearance.

FIG. 11 is an embodiment wherein, in the nozzle portion of cooling apparatus, a tube or a small structure 23 is partially arranged on the bottom surface of the cooling apparatus. Under normal circumstance, a tube without bend would be arranged on the side surface of the structure, but the problem associated with the N2 nozzle cannot solved by such a method because of a large wall-thickness of the structure and the presence of a mounting portion of the tube. The tube and the structure provided on the bottom surface, according to this embodiment has bent flow paths, and a connection portion for connecting the tube is configured so as not to be located on the undersurface. Here, a bent portion refers to a flow path for changing the direction of flow. This tube, having a large wall-thickness and high strength, and being inexpensively producible, it is particularly desirable. Consequently, by the present embodiment, this tube allows the inflow of jet into an especially narrow annular clearance. Regarding the present tube, by providing a fixing structure 24 for preventing oscillation and reducing hydraulic reaction force, problems such as oscillations and the like can be solved. Providing such a small tube or structure on the bottom surface allows the nozzle clogging due to erosion or clogged with foreign matter, to be replaced or repaired. Moreover, because of being a small structure arranged on the bottom surface, the present structure can efficiently flow jets into the narrow annular clearance. Furthermore, in the bend portion, jet flows run at a high flow speed on the outside thereof under centrifugal force, so that the jet constitutes a flow along the inner cylinder, thereby enhancing the convection in the annular clearance. The tube may be made of a metal, but use of an organic compound, such as Teflon®, as a material of the tube improves productivity. In this embodiment, nozzles are integrated with each other, and can also be removed from the main body of the apparatus.

As shown in FIG. 2A, under natural convection, high-temperature fluid moves to an upper portion of the annular clearance while low-temperature fluid moves to a lower portion thereof. In particular, in an upper portion of the annular clearance, high-temperature water stagnates. Therefore, installing the nozzles at an upper portions and stirring high-temperature water would promise to provide more effective cooling. In particular, as shown in FIG. 12, by providing a plurality of nozzles in a saddle-shaped tank, it is possible to efficiently blow jets into a high-temperature water portion and facilitate the layout of the nozzles. Also, installing jet nozzles for causing jet to rectlinearly proceed, to nozzle tips and rectlinearly spouting jet flows produces a higher effect. Additionally, a guide, a roller, or the like may be arranged in the saddle-shaped tank to facility positioning/layout of the nozzles.

In an embodiment shown in FIG. 13, a single or a plurality of nozzle tips is inserted into the annular clearance, and thereby an effective jet is flowed into the annular clearance. With nozzles provided in the reactor, the entire jet flows from the nozzles could not necessarily be flowed into the annular clearance. However, the present embodiment enables the entire jet flows to be flowed into the annular clearance. Furthermore, a use of this embodiment in combination with other embodiments enhances effect. Also, an insertion of a thermometer into the annular clearance improved measurement accuracy. In this case, if the nozzles are installed within the range of ±45 degrees with respect to the horizontal direction (direction from 3 o'clock to 9 o'clock) about the position of the riser pipe, then a larger insertion distance would be obtained.

FIG. 14 shows an embodiment in which a pad 12 is used. If the spacing of the annular clearance is very small and flow issued from the nozzles cannot be efficiently flowed into the annular clearance, this technique is effective because it does not require the thick-wall portion at the lower end. In this case, in order to guide flows into the annular clearance, it is advisable to install, at an proper location, a sealant 13 for preventing a leakage to the outside of the annular flow path. This technique can generate flows along the thermal sleeve 2, thereby producing a forced convection desirable for the annular clearance. In the embodiment shown in FIG. 13, an additional installation of a sealant 13 b on the piping side would produce a larger leakage prevention effect.

FIG. 15 shows IHSI method for promoting cooling effect with respect to the annular clearance by flows generated by suction flows. This embodiment exerts an effect particularly in the case of narrower annular clearance. Also, unlike jet flows as local flows, a suction flow promises to produce a stable high cooling effect. Moreover, installation of the thermometer 9 in the suction pipe allows a high-accuracy measurement.

FIG. 16 shows an embodiment in which the annular clearance is cooled by a submerged pump 14. In this case, piping and external circulation pump become unnecessary, and the construction is simplified. Even if flows are excited by moving the structure in the vicinity of the nozzle N2, the above-described simplification of construction allows similar cooling effect to be obtained.

In the PLR piping, there is a possibility that the cooling of nozzle to decontaminate may cause a problem besides the cooling of N2 nozzle. FIG. 17 shows an embodiment in which IHSI is applied to the nozzle to decontaminate 15. In this case, it is impossible to insert nozzles into water in the enclosed pipe. This being the situation, in this embodiment, after having decomposed the PLR piping, valves connected thereto, or the PLR pump, the nozzles 8 are inserted into PLR main piping 16. As a result, air could flow inside the piping. In the air, nozzles in limited direction cannot perform cooling, and therefore as shown in FIG. 17, it is necessary to arrange a large number of nozzles (pores), and radially pour water flows from the plurality of nozzles toward the inner surface of heated piping.

FIG. 18 shows an embodiment in which IHSI is applied to the nozzle to decontaminate 15, as well. When it is difficult to move nozzles into the nozzle to decontaminate 15, it is necessary to spout water flows from the PLR piping toward the nozzle to decontaminate 15, with the water flows spread in a spray shape or in a conical shape.

FIG. 19 shows a method for performing cooling operation from the outer surface of the piping. When the cooling apparatus cannot be inserted into the PLR piping, the cooling can be conducted from the outer surface of the piping. In this embodiment, possible coolants include liquids and gases, including water, nitrogen, argon, and so on. Particularly in order to reduce the base temperature of the piping, cooling by liquid nitrogen produces a large effect and improves operability. Also, previously cooling the piping and the inside thereof before the execution of IHSI operation, i.e., cooling them before heating them by a heater makes it possible to increase, even in a small quantity, the temperature difference between the inside and outside of the piping, thereby promising to bring about further effect. The technique according to this embodiment can be similarly utilized in other places including the N2 nozzle.

It has been verified by a computational fluid dynamics analysis that the increase in the number of revolutions of the pump in the PLR piping enables the cooling of the nozzle to decontaminate 15. In ordinary practice, IHSI operation is executed at the minimum pump revolution corresponding to a 20% flow rate, but at a pump revolution corresponding to a 25% flow rate or more, supply flow of the coolant increases. As a consequence, as indicated by the results of the computational fluid dynamics analysis, it is clear that the fluid temperature in the nozzle to decontaminate 15 reaches its saturation temperature. However, in the PLR piping in the reactor, a flange or an air vent cannot be installed from the viewpoint of safety ensuring and leakage prevention, so that air might stagnate in the nozzle to decontaminate 15. Unless air in the nozzle to decontaminate 15 can be eliminated, this embodiment could not be implemented.

As a method for removing air, the present invention executes the following means in an order of A→B→C→D as shown in FIG. 21. Furthermore, FIG. 22 shows an operational procedure. The area that most requires the removal of air is the nozzle to decontaminate. In general, non-condensing gas such as air, having a low density, stagnates at an upper portion of the nozzle to decontaminate 15 as shown in FIG. 21A, so that air cannot be removed by water flows. Non-condensing gas such as air is very low in thermal conductivity and heat transfer coefficient, and exerts a significant detriment to the execution of IHSI. In the present invention, the removal of air was performed using the following procedure. First, air that can be removed by water flows is eliminated by operating the PLR pump. Unlike an occasion when IHSI is executed, the PLR pump is stopped, or operated at a low revolution to facilitate the occurrence of boiling. Then, the nozzle to decontaminate 15 is heated. The order between the stop of the PLR pump and the heating of the heater may be reversed. The heating may be performed using a heater to be employed for the execution of IHSI, or another heater. For example, in the case where a pressure in the piping is about 0.25 MPa, when water in the piping arrives at its saturation temperature of 400 K, water evaporates as shown in FIG. 21B, vapors occur. At this time, a reduction in the opening of valves in front of and behind the nozzle to decontaminate, more facilitates the boiling inside the nozzle to decontaminate. The density of the water vapor under the above-described temperature and pressure conditions is approximately 1.37 kg/m², which is clearly smaller than the air's density of 2.18 kg/m². Consequently, air stagnant in an upper portion is gradually pushed out by water vapor. That is, because the evaporation of water increase the volume of the water by a factor of 1000, occurring water vapor easily pushes out the air inside the nozzle to decontaminate. As a result, as shown in FIG. 21C, the nozzle to decontaminate is filled with water vapor. Next, with the heater stopped and the output reduced, when the PLR pump is operated to increase flow rate, the air is blown off and the cooling effect is improved, whereby the water vapor decreases in temperature to thereby start to condense, as shown in FIG. 21D. When the water vapor decreases in temperature, it is totally subjected to a state change into water, so that the nozzle to decontaminate is filled with water. As a consequence, non-condensing gases, air, and the like can be perfectly removed from the nozzle to decontaminate. The state shown in FIG. 21D can be achieved by increasing the flow rate of the PLR pump without the need to stop the heater to reduce the output. Also, we can serve the purpose only by heating the heater. Here, the order between the operation of the PLR pump and the stop of the heater may be reversed. With the pump operated at the highest possible speed, the nozzle to decontaminate is overheated by the heater to execute IHSI. The order between the high-speed operation of the PLR pump and the heating of the heater may be reversed, although undesirable. Thus, it is possible to implement a reliable IHSI execution in a state in which air in stagnation portions in the nozzle to decontaminate and the like has been perfectly removed. When executing IHSI, it is necessary to enhance the cooling effect to suppress boiling, but when removing air, it is necessary to generate boiling to suppress the cooling effect. Therefore, the revolution of pump, the flow rate in the piping, and the opening of the valves are different between the time when executing IHSI and the time when removing air. As shown in FIG. 20A, under an operation at 20% flow rate of design rating, the inside of the nozzle to decontaminate 15 comes to a boil, so that the possibility of being able to execute IHSI is uncertain. The heating of the nozzle to decontaminate under a condition of 20% flow rate or less of design rating is considered as being a result of utilizing the present invention.

As is known, the fluctuating of flow causes a disturbance to a thermal boundary layer that has grown in a stable manner, and can thin the thermal boundary layer, as well as provides a fluid with a relatively high heat transfer coefficient. By adjusting the revolution of the PLR pump and/or the valve opening, it is possible to provide upstream side flow with a time-varying disturbance, and vary flow rate and pressure to increase heat transfer coefficient and circulation amount of water. Even when air is stagnant in the nozzle to decontaminate, means for varying flow rate and pressure is an effective method for removing air constituting an air accumulation. However, it is difficult to totally remove air only by the variation of flow rate.

When installing the cooling apparatus at an appropriate place, it is necessary to allow for the case where the piping has slight asperities, the case where it has slightly elliptic shape, and the case where individual piping sizes are diverse. Herein, as shown in FIG. 23, the nozzle position must be variable, and the nozzle installation portion must be configured so that and shape-variable tubes 17 and a support structure 18 are formed in one portion of the piping. This nozzle installation portion with the support structure has only to be of a shape-variable structure. Consequently, even in the case where the piping has slight asperities, the case where it has slightly elliptic shape, and the case where individual piping sizes are diverse, the positioning accuracy with respect to the nozzle position from which cooling water is to be supplied, and temperature measurement position is improved, thereby enabling proper cooling. Also, as shown in FIG. 1, when installing the nozzles in the horizontal direction, since there is a possibility of moving the nozzles, the present invention produces effect.

The above-described descriptions have focused on the cooling methods for the N2 nozzle and nozzle to decontaminate, for which the cooling conditions are severe when applying IHSI to the PLR piping as described above. However, these cooling methods are ones applicable to all other portions of the PLR piping, such as a crosshead portion, ring header end cap portion, takeoff bifurcation portion, tie-in portion of valves and pump, welding portion, which are structure-discontinuous portions with respect to other straight run of pipe.

The above-described embodiments can be applied to multiple pipe such as a feedwater nozzle, recombination T piping, low-pressure water injection nozzle, reactor core spray nozzle, and the like.

The above-described devices are guided by remote controlling, and hence, by installing sensors, cameras, or the like capable of verifying whether jet nozzles have been able to provided at predetermined positions, defects can be prevented when applying IHSI to an actual machine. In particular, it is necessary to verify whether cooling nozzles can be installed to the annular clearance of the N2 nozzle.

Moreover, observation of the annular clearance by miniature CCD (charge-coupled device) camera and video, pressure sensors, and the like allows the verification of boiling conditions and cooling effect.

On the other hand, as another example of conventional art, there is as induction heating stress improvement method disclosed in Japanese Patent No. 2624649. In this conventional art, partial water flows are formed by concentratedly spouting cooling water toward a base portion in an upper portion, and the N2 nozzle outer surface surrounding an annular space is heated to give a temperature difference to the nozzle wall, whereby residual stress is relaxed.

The above-described conventional art does have an enhanced cooling effect, but has given no consideration to the verification of a cooling effect when applying IHSI to an actual machine. In order to generate a flow by jetting a fluid into the narrow annular clearance of N2 nozzle, the jet nozzles must be installed at predetermined positions with high accuracy. However, since structures of the actual machine have manufacturing tolerances, the outer surfaces thereof might not be a perfect circle in the cross-section thereof. Additionally, the cooling apparatus must be inserted from a distant place above the pressure container of a reactor. It is therefore difficult to install the cooling apparatus at a predetermined location in the reactor. Also, there is a possibility that the jet nozzles may not be directed toward predetermined directions. Hence, it is necessary to verify and monitor, during or before application of IHSI to an actual machine, regarding whether jet flows have sufficiently flowed into the annular clearance to meet cooling performance. If the cooling is insufficient, the cooling apparatus must be reset to a proper location.

In the above-described conventional art, since water flows are concentrated at an upper portion, the flow velocity is lower at the side surface and a lower portion of the N2 nozzle than at the upper portion. The cooling performance is related to the magnitude of flow velocity; the larger the flow velocity, the higher is the cooling effect. This causes a possibility that the cooling performance decreases at the side surface and the lower portion where the flow velocity decreases. At the portions with cooling performance reduced, hot spots (local portions with high temperature) occur, so that a reduction in IHSI effect is predicted.

Therefore, in applying IHSI to the N2 nozzles or the like with a narrow annular clearance, there occurs challenges as follows: 1) monitoring of cooling performance when executing IHSI, and 2) ensuring of uniform cooling performance.

In the conventional arts, metal temperatures have been measured to check IHSI execution status. However, there has been a possibility that it cannot be determined, by the measurement of metal temperature, whether the cooling performance is sufficient up to a burnout (film boiling). To solve this problem, in the present invention, a thermometer is installed in or around IHSI cooling apparatus to measure fluid temperature during IHSI operation. In other words, fluid temperature is used as an index of cooling performance.

On the other hand, when measuring fluid temperature, it is necessary to raise temperature after having cooled a heated portion and measure the temperature of outflowing fluid. Here, since a thermometer is inserted in a complicated reactor, the range within which the thermometer can be installed is limited. This being the case, by tests and a computational fluid dynamics analysis, the present inventors examined the relationships among the installation positions of jet nozzles, that of thermometer, and the outflow direction of fluid. The results are shown in Table 1. TABLE 1 Jet nozzle Thermometer Outflow installation installation direction of Assess- positions position fluid Examinations ment Upper Portion Upper portion Lower portion Fluid outflow direction and x thermometer installation position are mutually different Upper portion Horizontal Lower portion Fluid outflow direction and x thermometer installation position are mutually different Upper Portion Lower portion Lower portion Not suited for measurement of x high-temperature fluid Lower portion Upper portion Upper portion It is difficult to install jet x nozzles at lower portions Lower Portion Horizontal Upper portion Fluid outflow direction and x thermometer installation position are mutually different Lower Portion Lower portion Upper portion Fluid outflow direction and x thermometer installation position are mutually different Horizontal (1 place) Upper portion Horizontal Fluid outflow direction and x thermometer installation position are mutually different Horizontal (1 place) Horizontal Horizontal Not suited for measurement of x high-temperature fluid Horizontal (1 place) Lower portion Horizontal Fluid outflow direction and x thermometer installation position are mutually different Horizontal (2 or Upper portions Upper and Optimum ∘ moreplaces) lower portions Horizontal (2 or Horizontal Upper and Fluid outflow direction and x moreplaces) lower thermometer installation portions position are mutually different Horizontal (2 or Lower portions Upper and Not suited for measurement of x moreplaces) lower high-temperature fluid portions

Since high-temperature water moves upward, in order to measure higher fluid temperature, the thermometer must disposed at an upper portion. Also, in order to measure the temperature of the fluid of which the temperature has been raised by cooling the heated portion, the outflow direction of the fluid and the installation position of the thermometer must be the same. Moreover, it is difficult to dispose the thermometer and the jet nozzles at lower portions. From the above-described studies, the present inventors have found out, as new findings, that disposition of jet nozzles at two places or more in the horizontal direction, as well as disposition of the thermometer at an upper portion, enable IHSI execution and monitoring by an optimum fluid temperature measurement (refer to Table 1).

In advance (i.e., before executing IHSI), the relationship between the fluid temperature distribution in the annular clearance and the temperature of fluid flowing out therefrom can be determined by a computational fluid dynamics analysis and tests. If the temperature measured by the thermometer is the determined temperature, it is considered that the heated surface is being cooled by the jet nozzles under a forced convection. On the other hand, if the temperature measured by the thermometer is shifted from the determined temperature, it is considered that the forced convection by the jet nozzles is not effectively working.

FIG. 24 shows a flowchart showing IHSI execution procedure. First, in advance, the relationship between the temperature distribution in the annular clearance and outflowing fluid is derived. Next, nozzles are installed for executing IHSI. Thereafter, the execution of IHSI is performed. Herein, the temperature of outflowing fluid is measured. Then, using the relationship between the temperature distribution in the annular clearance and outflowing fluid that have been derived, the temperature distribution in the annular clearance is estimated. If the temperature distribution in the annular clearance is within a predetermined range, the execution of IHSI is kept on, as it is. On the other hand, if the temperature distribution in the annular clearance is out of the predetermined range, resetting (or fine adjustment) of the nozzles are performed. After predetermined execution, the execution of IHSI is completed. Here, if fluid in the annular clearance comes to a boil (film boiling), cooling becomes impossible, and therefore it is particularly important that the temperature of the fluid in the annular clearance is not more than the saturation temperature thereof.

Next, description will be made of the achievement of uniform cooling performance. If the jetting direction of fluid is definite, there occur places where the main flow of jet flows pass and places where they do not pass, so that the cooling performance with respect to the annular clearance becomes nonuniform. Also, at places where the main flow of jet flows pass, hot spots occur, so that film boiling is prone to occur. Such being the case, the present inventors studied methods for making cooling performance uniform. As a result, the inventors have found out, as new findings, that a method for oscillating jet flows in an up-and-down direction is effective in making cooling performance uniform. Additionally, it has been founded out that spouting jet flows, with the jet nozzles arranged in symmetry, makes the jet flows unstable to thereby oscillate them. Therefore, by vibrating jet flows in the up-and-down direction with the jet nozzles arranged in symmetry, the cooling performance can be made stable, resulting in suppressed hot spots. In reality, because it is difficult to arrange the jet nozzles at lower portions, the jet nozzles is arranged in symmetry in the horizontal direction (i.e., direction from 3 O'clock to 9 o'clock), as well as the jet flows are oscillated in the up-and-down direction, whereby the cooling performance is rendered uniform.

From the foregoing, the present inventors drew a conclusion that arranging the jet nozzles in symmetry in the direction from 3 O'clock to 9 o'clock (i.e., horizontal direction), and disposing the thermometer in the direction of 12 o'clock (i.e., at an upper position) in properly monitoring the execution of IHSI and making cooling performance uniform.

Now, with reference to FIG. 25, description will be made of the IHSI N2 nozzle cooling method to which the present invention is applied. FIG. 25 is a structural view of a cooling apparatus 107 for applying the present invention, and an N2 nozzle system as an application object. The N2 nozzle system comprises an N2 nozzle 101, a thermal sleeve 102 inside the N2 nozzle 101, and a riser pipe 103 serving as a jet pump. A welding portion 104 in the N2 nozzle 101 is subjected to relaxation of residual stress by the execution of IHSI. The execution of IHSI is implemented by heating the outer surface of metal by a heater 105 and cooling the inner wall of the metal by inner water flows to give a temperature gradient in the radial direction, to the nozzle wall. When the piping is of a pure straight pipe, the inner surface of the piping is sufficiently cooled. However, in the annular clearance 6 on the piping inner surface at the welding portion, since the flow stagnates, fluid temperature increases, so that the inner surface of the piping could not sufficiently cooled. With such being the situation, in this embodiment, cooling water is spouted from the jet nozzles 108 provided in the cooling apparatus 107 toward an annular clearance 106, and the inner surface of the heated N2 nozzles 101 is cooled.

The cooling apparatus 107 is guided by remote from an upper portion of the reactor. It is therefore necessary to verify whether the cooling apparatus 107 has been installed at a predetermined place. In this embodiment, it is verified whether the cooling apparatus 107 has been installed at the determined place by measuring the temperature of the fluid of which the temperature has been raised by cooling the heated portion, before and during the execution of IHSI. If it is determined that the cooling apparatus 107 has not been installed in a proper place, the cooling apparatus 107 is reset (or finely adjusted).

In this embodiment, in order to measure a fluid temperature, the cooling apparatus 107 has a thermometer 109. Here, the jet nozzles 108 are arranged at the center in the horizontal direction (direction from 3 o'clock to 9 o'clock), and the thermometer 109 is disposed at an upper portion (12 o'clock direction) in a state in which their peripheral positions are shifted from each other. The cooling water is driven by a pump 110, and is spouted from the jet nozzles 108 through piping 111. According to this embodiment, as indicated by arrows in FIG. 25A, the jet flows spouted from the jet nozzle 108 travels toward welding portion, and thereafter, the jet flows cool the heated portion to thereby rise in the temperature thereof, as well as flow out in the reactor from the upper and lower sides of the annular clearance 106 (the directions of 0 o'clock and 6 o'clock) FIG. 26 is a top view of an embodiment in which the present invention is applied to the N2 nozzle. The jet nozzle 108 is tilted by 0 degrees under restriction on the structure. Water flows spouted from the cooling apparatus 107 flow toward the welding portion 104 along the horizontal portion (the direction from 3 o'clock to 9 o'clock) of the annular clearance 106, and after having collided against the base portion, travel separating into the upper and lower sides. The upside flow flows out from the annular clearance 106 into the reactor. At this time, the temperature of outflowing fluid is measured by the thermometer 109 disposed at the upper portion. Since high-temperature fluid stagnates in an higher portion, it is desirable that the thermometer 109 be disposed at an upper portion and measure the temperature of fluid flowing out from the upper portion to thereby monitor IHSI execution status.

FIG. 27 shows the relationship between the installation angle of the jet nozzles 108 and the outflowing velocity at an upper portion. Here, the “outflowing velocity” refers to the velocity of fluid (jet flow) heading from the annular clearance 106 into the reactor. As shown in FIG. 27, the larger the installation angle θ (refer to an upper-right figure), the lower is the outflowing velocity at an upper portion. If the region of θ=40 degrees is exceeded, the outflow of fluid (jet flow) from the upper side becomes nonexistent. Hence, in the region of θ>40 degrees, it is difficult to measure the temperature of outflowing fluid that has cooled the heated portion of the annular clearance 106 by the thermometer 109 provided at an upper portion. When the jet nozzles 108 is arranged within the range of +40 degrees from the horizontal direction (the directions of 3 o'clock and 9 o'clock), the upward direction (direction of 12 o'clock) becomes an outflow direction. Therefore, in order to measure the temperature of fluid flowing out from the upper portion, the thermometer 109 for use in monitoring is installed at an upper portion (within the range of ±50 degrees from the direction of 12 o'clock). In this manner, separately installing the jet nozzles 108 and thermometer 109 in the peripheral direction allows an effective measurement of fluid temperature.

The number of jet nozzles (or nozzle) 108 is not limited, but when a plurality of them is used, they must be arranged in a substantially symmetric manner. It is virtually impossible to arrange the jet nozzles 108 or thermometer 109 at lower portions (6 o'clock position). However, as shown in FIG. 25A, by lowering the positions of jet nozzles 108 by D from the horizontal direction (direction from 3 o'clock to 9 o'clock) within the range observable from the upper side, it is possible to reliably flow out the fuel from the upper position. Here, the position of the jet nozzles 108 can be made lower than the horizontal direction (direction from 3 o'clock to 9 o'clock) if the positions of the jet nozzles 108 are located outside the tangent (dotted line in FIG. 25B) at positions of 3 o'clock and 9 o'clock. Thus, more reliable monitoring of the execution of IHSI can be achieved. In this case, as shown in FIG. 26, tilting the jet nozzles 108 by θ degrees allows jet flows to smoothly flow into the annular clearance 106.

Furthermore, installing the jet nozzles 108 within the range of ±40 degrees from the horizontal direction (3 o'clock direction and 9 o'clock direction), promises to produce a uniform cooling effect. This effect will be described using the computational fluid dynamics analysis results. FIGS. 28A and 28B each show vectors of flows in the annular clearance 106 when the jet nozzles 108 are arranged within the range of ±40 degrees from the horizontal direction (3 o'clock direction and 9 o'clock direction). When the jet nozzles 108 are arranged in the horizontal direction (3 o'clock direction and 9 o'clock direction), flows in FIG. 28A and those in FIG. 28B alternately oscillatingly occurs, and alternately cool the upper portion and lower portion of the heated portion as shown in FIGS. 28A and 28B. This makes it possible to uniformly cool the heated portion. Because this phenomenon holds when fluid flows out toward each of the upper portion and lower portion, as shown in FIG. 27, it is necessary to arrange the jet nozzles 108 within the range of ±40 degrees from the horizontal direction (3 o'clock direction and 9 o'clock direction).

As described above, in order to monitor an execution status of IHSI, and achieve uniform cooling performance by jet flow oscillation, it is necessary to arrange the jet nozzles 108 within the range of ±40 degrees from the horizontal direction (3 o'clock direction and 9 o'clock direction), and dispose the thermometer 109 (sensor) within the range of ±50 degrees from an upper portion (12 o'clock position). Thereby, it is possible to secure inner surface cooling when applying IHSI to an actual machine, reliably relax residual stress in the nozzle welding portion of the pressure container of a reactor, and thereby supply a more safe nucleate power plant. 

1. An induction heating stress improvement method in a nuclear power plant, the method comprising: verifying a cooling effect with respect to the inner surface of piping by measuring a fluid temperature that has been raised by external heating of the piping when applying the induction heating stress improvement method to an actual machine.
 2. An induction heating stress improvement method in a nuclear power plant, the method comprising: verifying a cooling effect with respect to the inner surface of piping of a recirculation inlet nozzle by measuring a fluid temperature that has been raised by external heating of the recirculation inlet nozzle when applying the induction heating stress improvement method to an actual machine, using a thermometer provided in a cooling apparatus of the recirculation inlet nozzle.
 3. An induction heating stress improvement method in a recirculation inlet nozzle of primary loop recirculation piping (hereinafter referred to as PLR piping) in a nuclear power plant, the method comprising: installing at least one jet nozzle of a cooling apparatus only within the range of ±45 degrees from a horizontal direction (3 o'clock direction and 9 o'clock direction) of an annular clearance of the recirculation inlet nozzle, about the center of the annular clearance in the horizontal direction, to thereby promote a cooling effect.
 4. An induction heating stress improvement method in a recirculation inlet nozzle of PLR piping in a nuclear power plant, the method comprising: installing a thermometer only within the range of ±45 degrees from an upper portion (0 o'clock position) of an annular clearance; and installing at least one jet nozzle of a cooling apparatus only within the range of ±45 degrees from a horizontal direction (3 o'clock direction and 9 o'clock direction) of the annular clearance, about the center of the annular clearance in the horizontal direction, to thereby promote a cooling effect.
 5. An induction heating stress improvement method in a recirculation inlet nozzle of PLR piping in a nuclear power plant, the method comprising: tilting the tip of at least one nozzle so as to include a tilt component in a tangential direction to an inner cylinder, to thereby promote a cooling effect.
 6. An induction heating stress improvement method in a recirculation inlet nozzle of PLR piping in a nuclear power plant, the method comprising: tilting a jetting direction of the tip of at least one nozzle in a direction toward the center of an inner cylinder, to thereby promote a cooling effect.
 7. A cooling apparatus using an induction heating stress improvement method in a recirculation inlet nozzle of PLR piping in a nuclear power plant, the cooling apparatus comprising: a cave hole serving as a nozzle for use in jetting a coolant, the cave hole being formed in a structure constituting the bottom of the cooling apparatus in the vicinity of the inner cylinder of a recirculation inlet nozzle, wherein the cave hole that has a narrowed portion and a enlarged portion and that is not axisymmetric.
 8. A cooling apparatus using an induction heating stress improvement method in a recirculation inlet nozzle of PLR piping in a nuclear power plant, the cooling apparatus comprising: a header tank installed in a structure constituting the bottom of the cooling apparatus in the vicinity of the inner cylinder of a recirculation inlet nozzle, wherein a coolant is flowed into an annular clearance from a plurality of nozzles (pores) disposed at lower portions of the header tank to thereby promote a cooling effect of the cooling apparatus.
 9. A cooling apparatus using an induction heating stress improvement method in a recirculation inlet nozzle of PLR piping in a nuclear power plant, the cooling apparatus comprising: a first structure that is installed to a second structure constituting the bottom of the cooling apparatus (main body) in the vicinity of the inner cylinder of the recirculation inlet nozzle, the first structure being smaller than the second structure and having a bent portion; and wherein a coolant is flowed from a nozzle of the first structure into an annular clearance to thereby promote a cooling effect.
 10. An induction heating stress improvement method in a recirculation inlet nozzle of PLR piping in a nuclear power plant, the method comprising: flowing a coolant into an annular clearance along a flow path formed between a structure (pad) having a sealing mechanism and arranged along an inner cylinder, and the outer surface of the inner, whereby a cooling effect is improved.
 11. An induction heating stress improvement method in a recirculation inlet nozzle of PLR piping in a nuclear power plant, the method comprising: inserting a nozzle of a cooling apparatus or a pipe into an annular clearance to thereby promote a cooling effect.
 12. An induction heating stress improvement method in a recirculation inlet nozzle of PLR piping in a nuclear power plant, the method comprising: installing a fluid suction portion in the outlet of an annular clearance, and thereby improving the cooling effect with respect to the annular clearance by flow generated by the suction flow.
 13. An induction heating stress improvement method in a recirculation inlet nozzle of PLR piping in a nuclear power plant, the method comprising: exciting flow by swinging a structure in the vicinity of the recirculation inlet nozzle, to thereby promote a cooling effect.
 14. An induction heating stress improvement method in a recirculation inlet nozzle of PLR piping in a nuclear power plant, the method comprising: exciting flow in the vicinity of the recirculation inlet nozzle by a submerged pump or a stirrer, to thereby promote a cooling effect.
 15. The induction heating stress improvement method according to claim 3, the method comprising: allowing an enhancement of the accuracy of the method by the optimization of a method for supplying cooling water to the inner surface of piping and a verification of a cooling effect with respect to the inner surface of piping, by measuring a fluid temperature that has been raised by external heating of the piping when applying the induction heating stress improvement method to an actual machine.
 16. An induction heating stress improvement method in a nozzle to decontaminate of PLR piping in a nuclear power plant, the method comprising: decomposing front and rear valves, primary loop recirculation pump (hereinafter referred to as PLR pump), or pipes, and then inserting a cooling nozzle into a PLR main piping; and directing the nozzle toward a heated portion on the inner surface of piping in the nozzle to decontaminate, and jetting cooling water from inside the nozzle to decontaminate or from the PLR main piping, in a radial manner, in a spray shape, in a hollow-cone shape, in a filled-cone shape, or in a mist shape, to thereby promote a cooling effect with respect to the inner surface of the nozzle to decontaminate.
 17. An induction heating stress improvement method in a nuclear power plant, the method comprising: cooling piping and an inner fluid from the outer surface of the piping except a heater installation portion, to thereby promote a cooling effect.
 18. An induction heating stress improvement method in a nozzle to decontaminate of PLR piping in a nuclear power plant, the method comprising: cooling piping and an inner fluid from the outer surface of the piping before executing the induction heating stress improvement method, to thereby promote a cooling effect.
 19. An induction heating stress improvement method in a nozzle to decontaminate of PLR piping in a nuclear power plant, the method comprising: operating a PLR pump at a revolution number of 25% or more of a revolution rating, to thereby promote a cooling effect.
 20. An induction heating stress improvement method in piping in a nuclear power plant, the method comprising: heating the piping before executing the induction heating stress improvement method; and after having cooled the piping, executing the induction heating stress improvement method.
 21. An induction heating stress improvement method in piping in a nuclear power plant, the method comprising: heating water in a nozzle to decontaminate up to a saturation temperature thereof before executing the induction heating stress improvement method; and after having cooled the water, executing the induction heating stress improvement method.
 22. An induction heating stress improvement method in piping in a nuclear power plant, the method comprising: flowing water through PLR piping; after having heated a nozzle to decontaminate, increasing a flow rate of water; and heating the nozzle to decontaminate to thereby execute the induction heating stress improvement method.
 23. An induction heating stress improvement method in piping in a nuclear power plant, the method comprising: stopping flow in a PLR piping, and heating a nozzle to decontaminate; and flowing water through the piping to thereby execute the induction heating stress improvement method.
 24. An induction heating stress improvement method in piping in a nuclear power plant, the method comprising: after having heated a nozzle to decontaminate, heating the nozzle to decontaminate, with the opening of valves in front of and behind the nozzle to decontaminate increased; and executing the induction heating stress improvement method.
 25. An air removal technique in an induction heating stress improvement method in piping in a nuclear power plant, the technique comprising: heating a nozzle to decontaminate by fluid at a flow rate of 20% or less of a design rating.
 26. The induction heating stress improvement method according to claim 21, wherein the method is executed by applying it to closed piping, cap, or recirculation inlet nozzle.
 27. An induction heating stress improvement method in nuclear and thermal power plants, the method comprising: intentionally varying or fluctuating the flow rate or the pressure of fluid in piping by valves or the revolution number of a pump, during the heating of the piping by a heater.
 28. An induction heating stress improvement method in PLR piping in a nuclear power plant, the method comprising: intentionally varying or fluctuating the flow rate or the pressure of fluid in the piping by inlet and exit valves of a PLR pump or the revolution number of the PLR pump, during the heating of the piping by a heater.
 29. An induction heating stress improvement method in PLR piping in a nuclear power plant, the method comprising: varying the fluid pressure in the piping by seal purge water of a PLR pump, during the heating of the piping by a heater.
 30. An induction heating stress improvement method in PLR piping in a nuclear power plant, wherein a member for supporting at least one nozzle of a cooling apparatus for the inner surface of the piping is configured to be able to change its shape.
 31. An induction heating stress improvement method in PLR piping in a nuclear power plant, the method comprising: allowing an enhancement of the accuracy of the method by the optimization of a method for supplying cooling water and a verification of a cooling effect, by according to claim
 1. 32. The induction heating stress improvement method according to claim 1, wherein the method is applied to a multiple pipe such as a reactor feed water nozzle, recombination T piping, a low-pressure spray nozzle, and a reactor core spray nozzle.
 33. The induction heating stress improvement method according to claims 1, the method comprising: a cooling apparatus, and in particular, an apparatus capable of detecting and verifying an installation position of at least one nozzle.
 34. An induction heating stress improvement method in PLR piping in a nuclear power plant, the method comprising: verifying a cooling effect by image equipment such as a camera and a video, or a pressure sensor.
 35. An induction heating stress improvement method in a nozzle of a nucleate reactor pressure vessel for a nuclear power plant, the method comprising: verifying a cooling effect of the nozzle portion by measuring a fluid temperature or a pressure when applying the induction heating stress improvement method to an actual machine, or when performing preliminary heating, or before executing the induction heating stress improvement method.
 36. An induction heating stress improvement method in a nozzle of a nucleate reactor pressure vessel for nuclear power, the method comprising: installing the measurement sensor used in claim 1 in a cooling apparatus having jet at least one nozzle.
 37. An induction heating stress improvement method in a recirculation inlet nozzle of PLR piping in a nuclear power plant, the method comprising: installing at least one jet nozzle of a cooling apparatus only within the range of ±40 degrees from a horizontal direction (3 o'clock direction and 9 o'clock direction) of an annular clearance of the recirculation inlet nozzle, about the center of the annular clearance in the horizontal direction, to thereby promote a cooling effect by water flows from the jet nozzle.
 38. An induction heating stress improvement method in a recirculation inlet nozzle of PLR piping in a nuclear power plant, the method comprising: installing at least one jet nozzle of a cooling apparatus only within the range of ±40 degrees from a horizontal direction (3 o'clock direction and 9 o'clock direction) of an annular clearance of the recirculation inlet nozzle, about the center of the annular clearance in the horizontal direction; and installing a thermometer or a pressure meter only within the range of ±50 degrees from an upper portion (0 o'clock position) of the annular clearance. 